Calretinin (protein 10) was isolated and purified in our laboratory last year. The calretinin antibody has been successfully employed in mapping the localization of this brain specific neuronal calcium binding protein. A detailed histochemical mapping of calretinin was completed in the rat forebrain. Results have identified calretinin containing neurons in many brain nuclei including for example, the habenula, interpeduncular n., lateral mammillary n., anterior n. of the thalamus and dopamine cells of the substantia nigra compacta. Pathways emanating from these and other groups of labeled cells also display calretinin immunoreactivity. A quantitative radioimmunoassay was developed and successfully employed to provide estimates of calretinin concentrations in numerous brain regions. Studies have also expanded results indicating calretinin as a major sensory cell protein. Calretinin was identified in the spiral ganglion and inner hair cells of the cochlea and in a subpopulation of vestibular ganglion and hair cells. Kinetic studies of calcium binding to calretinin suggest that it contains 5-6 calcium binding sites with an apparent kd of 0.1 (mu)M calcium. Pilot studies examining the effect of excitatory amino acid receptor agonists on fetal cortical cells in culture have indicated a selective survival of the calretinin containing neurons, suggesting that calretinin may act to buffer intracellular calcium and thus prevent some forms of neuronal damage.